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Old 13-12-2016, 07:42   #1
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Redundant GPS antennas on NMEA2000

Hello all,

I'm new to NMEA2000 and I'm installing a B&G Zeus2 plus 3G radar on to an existing backbone on my boat. It seems like it will be pretty straightforward to integrate the new units with the system, which already has SOG from GPS (as well as depth, wind, water temp, etc.) that it shows on a Maretron display.

The boat currently has two external GPS antennas on the bimini frame. I believe one was for the old radar (which I've removed) and the other I believe is for the NMEA2000 system. It will now have a third internal GPS in the Zeus plotter.

My question: should I remove redundant units wherever possible, or does it make sense to keep them for a backup source of data? I'm guessing that the radar GPS is now completely useless, but should the other antenna stay for redundancy/backup? What does the system do if two GPS receivers provide slightly conflicting information? Does it average them somehow?

Thanks,
Jack
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Old 13-12-2016, 08:17   #2
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Re: Redundant GPS antennas on NMEA2000

My opinion is to keep it, test it separately from what you have now and verify that it works with the system...

Then unplug, and coil the wire back at your nmea bridge so that if you have an electrical failure/lightening strike your back-up isn't plugged into the rest of the system and it might live through it.
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Old 13-12-2016, 08:24   #3
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Re: Redundant GPS antennas on NMEA2000

My Zeus will use the Vesper for GPS if I chose to, the available sources will be displayed and available. In my case the Vesper receives more satellites and has a greater accuracy than the Zeus internal GPS, so I use the Vesper.
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Old 13-12-2016, 08:28   #4
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Re: Redundant GPS antennas on NMEA2000

We have an external gps in addition to the inbuilt zeus2 gps.

The zeus picks up and registers the networked sensors. I assume if it has detected and can receive data from the external gps then i would expect it not to read from the inbuilt gps. The input is tied to a registered sensor.

Averaging of multiple gps data makes no sense. This could introduce errors and degrade a correct sensor input if one sensor was bad. That's not safety critical logic.

We haven't yet tested the variance between the internal and external sensor. I don't know if the zeus2 will register more than one gps. Someone else on the forum might have checked for this configuration.

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Old 13-12-2016, 08:48   #5
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Re: Redundant GPS antennas on NMEA2000

My advice is to keep them for redundant source of GPS data. However, I like Zachís suggestion of keeping at least one disconnected and available in case of a lightening strike. Personally, I experienced this in Oyster Bay several years ago. I have an extensive NMEA 2000 network with multiple GPSís connected. Slight conflicts in data between GPSís can be a problem, but the Zeus should let you choose which GPS itís going to listen to. I like making the most accurate GPS the primary navigator and selecting this in the chartplotter software. Make all listeners on the network use the same GPS source. This should eliminate any possible conflict. The more disturbing conflict is with your heading source or compass. All listeners on the network should be programed to use the same electronic compass, if you have more then one. There is nothing more irritating then looking at one display and seeing a heading number that conflicts with a second display. Autopilots are especially sensitive to getting the heading data without conflict or delay.
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Old 13-12-2016, 09:22   #6
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Re: Redundant GPS antennas on NMEA2000

In your setup screens for your displays there should be an option to select the source for each input. List the GPS units and select the one you want to use.

As stated, If they all still work, take at least one down and keep it un-connected as a spare. If your new radar can use the internal GPS, then it is up to you as to whether or not to keep the other external. If the external is more sensitive or picks up more satellites, select it.

If your VHF DSC or other separate displays use the external GPS, I'd keep it up, especially if the new chartplotter is going to be a removeable mount. That way you have the GPS position all the time for an emergency, even if the chartplotter is not mounted.
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Old 13-12-2016, 09:38   #7
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Re: Redundant GPS antennas on NMEA2000

Super quick and clear answers and a rare consensus! A+ service, thanks everybody!
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Old 13-12-2016, 12:11   #8
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Wink Re: Redundant GPS antennas on NMEA2000

I am in a somewhat similar situation with upgrading instruments on my newly acquired (well a year ago) 1975 DownEaster 38. Not so much as you have, but there is an old Garmin GPS/Chart Plotter with external GPS antenna. I am about to install a B&G Vulcan 7 Chart plotter which, like the Zeus, has an internal GPS antenna, but Navico recommend an external GPS/Compass unit connected via the NM2K network. The GPS source (internal or external) is selected when you set up the chart plotter.
I am thinking about leaving the Garmin with external antenna in place as a back up with display at the chart table and put the Vulcan at the helm. So I'll have two GPS antennas: One connected to the Garmin, the other to the NM2K network.
If you have removed the radar unit I would think that the companion GPS antenna would be pretty useless since it is not on the NM2K network. What use can it have now? You might check with Navico people to see if they recommend their GPS Antenna with built in Heading Sensor.
Not sure if this helps you, but it helps me to write out my own situation!
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Old 23-12-2016, 23:03   #9
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Unhappy Re: Redundant GPS antennas on NMEA2000

Quote:
Originally Posted by OrangeCrush View Post
Hello all,

I'm new to NMEA2000 and I'm installing a B&G Zeus2 plus 3G radar on to an existing backbone on my boat. It seems like it will be pretty straightforward to integrate the new units with the system, which already has SOG from GPS (as well as depth, wind, water temp, etc.) that it shows on a Maretron display.

Thanks,
Jack
I am also installing a Zeus2 7 with 3G Radar, but with a new NM2K network. I plan to add WiFi, but the Zeus2 7 has only one Ethernet port, so I'll need the NEP-2 Network Expansion Port. Do you have the same setup? Are you getting the NEP-2 also? Pretty expensive for a switch, but the data streams must be pretty complex, so who am I to argue?
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Old 23-12-2016, 23:36   #10
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Re: Redundant GPS antennas on NMEA2000

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Do you have the same setup? Are you getting the NEP-2 also? Pretty expensive for a switch, but the data streams must be pretty complex, so who am I to argue?
Hmm I actually hadn't given that part of it to much thought yet but yes I think I will need that, along with the wifi antenna too, right?. Yeah it sure does add up. Everything on a boat is pricey but the electronics are out of control. I'll probably end up completing the main radar/plotter install first and add the wifi a little bit later when all my other boat work is neatly wrapped up and my bank account is replenished...
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Old 24-12-2016, 00:46   #11
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Re: Redundant GPS antennas on NMEA2000

Great question as I am in a similar situation trying to figure out how to allocate 3 GPS sensors

GPS antenna for FURUNO GP-33
GPS antenna for VESPER AIS
GPS built in FURUNO TZ Touch 2

My understanding from Jeff is that the Vesper GPS is a specialized unit for AIS module and should not be substituted.

If the built in Touch 2 GPS has good reception, I will keep the GP-33 networked to FURUNO Instruments and PC.

Thus keeping the MFD as a stand alone position display with the least movement.

Very open to opinions and advice on this?
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Old 24-12-2016, 06:52   #12
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Re: Redundant GPS antennas on NMEA2000

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Great question as I am in a similar situation trying to figure out how to allocate 3 GPS sensors

GPS antenna for FURUNO GP-33
GPS antenna for VESPER AIS
GPS built in FURUNO TZ Touch 2

My understanding from Jeff is that the Vesper GPS is a specialized unit for AIS module and should not be substituted.

If the built in Touch 2 GPS has good reception, I will keep the GP-33 networked to FURUNO Instruments and PC.

Thus keeping the MFD as a stand alone position display with the least movement.

Very open to opinions and advice on this?
The AIS will use its attached GPS - Class B devices are required to so do. Some AIS devices can also repeat their GPS info on N2K for use by other devices. You can almost always turn it on or off.

I would use the GP-33 as the primary navigation GPS, mostly because it has an external antenna and will get a better and more reliable fix than the internal device in the TZ. You do this in the TZ setup selecting the GP-33 as the preferred source for position, SOG, and COG. If the GP-33 fails, the TZ will revert to whatever else it can find, either its internal GPS or the AIS GPS. But I'd make the best GPS the primary, and I think that's your GP-33.

Evey boat and installation will be different, but I have a TZ-2 on a 28' open power boat with hardtop. The TZ is console mounted, and struggles to get a GPS fix. Other boats get a fix just fine, but my point is that it can be flaky getting a stable fix from the built-in GPSs in MFDs. So I would always use it as a backup, never the primary.

Selecting your data source is straight forward with the TZ. There are drop down lists of available devices and you pick which you want. Most N2K devices work this way. Just be aware that if you end up using any Maretron display devices, they do data source selection differently from everyone else. They do it exclusively based on Device Instance Number, or Data Instance Number. They refer to these as Unique Instance Numbers, but unless you know way more about N2K than you should ever need to know, you will not know the Unique Instance is a Device Instance or a Data Instance.

But without diving into way more than I'm sure you care about, this will have a direct impact on your GPSs. Each GPS will have to be assigned a unique Device Instance. How this is done depends on the product, and unfortunately many devices cannot change their Device Instance even though it's a required feature in N2K. AIS devices derived from SRT, which is pretty much all AIS devices, cannot change their instance number. It will always be zero. This means you need to change the instance number of all the other GPSs, and hope it's possible to do so.

Once you have assigned Device Instance Numbers to each GPS, then in the Maretron display product you select which Instance number's data you want it to use. This means you need to keep track of all your devices and what instance number you assigned to it so you know which to select.

I've discussed this at length with Maretron, and although they have their reasons for doing it this way, I personally find it to be a royal PITA.

And if you don't have any Maretron products, well, never mind.
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Old 24-12-2016, 09:07   #13
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Re: Redundant GPS antennas on NMEA2000

Thanks Greatly Tanglewood......
I don't get much reliable interface support here in the Philippines on Furuno.

Local Technicians have more of a 'connect and see' approach to interface as their experience with new installations are limited

... so I will need to learn all of this, when I light up the system for the first time in January after the new consoles are installed.

If OK I may PM you with a basic layout, Interface and wiring diagrams as a pre-check before we test.
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Old 24-12-2016, 09:10   #14
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Re: Redundant GPS antennas on NMEA2000

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Thanks Greatly Tanglewood......
I don't get much reliable interface support here in the Philippines on Furuno.

Local Technicians have more of a 'connect and see' approach to interface as their experience with new installations are limited

... so I will need to learn all of this, when I light up the system for the first time in January after the new consoles are installed.

If OK I may PM you with a basic layout, Interface and wiring diagrams as a pre-check before we test.
Sure, send away.
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Old 24-12-2016, 09:48   #15
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Re: Redundant GPS antennas on NMEA2000

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I'll probably end up completing the main radar/plotter install first and add the wifi a little bit later when all my other boat work is neatly wrapped up and my bank account is replenished...
Interesting. I plan to set up WiFi before radar so that I can mirror the Zeus display (at chart table) from the helm or any where else on the boat. Once that is operational I'll go to the radar. Have you decided on a location for the dome?
As to GPS the Navico man told me that their ZG100 is essential to get accurate heading data into the system. You might want to look into that, too.
Head spinning yet? Mine is!
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